Field of the invention
The present invention relates to a window glass heating apparatus for heating a window glass of a vehicle to prevent the window glass from being clouded or remove a cloud of the window glass.
Description of the related art
There is known a window glass heating apparatus for heating a window glass of a vehicle to prevent the window glass from being clouded or remove a cloud of the window glass. The window glass heating apparatus has an electric heating wire and a switch operated by a user of the vehicle to start and stop an execution of an energization control for controlling an energization of the electric heating wire. Hereinafter, this window glass heating apparatus will be referred to as “the conventional apparatus”.
When the switch is operated by the user of the vehicle while the energization control is not executed, the conventional apparatus starts the execution of the energization control to start the energization of the electric heating wire. Thereafter, the conventional apparatus stops the energization of the electric heating wire when a predetermined time has elapsed after starting the energization of the electric heating wire.
The conventional apparatus determines the predetermined time on the basis of an atmospheric temperature outside of the vehicle, a difference between the atmospheric temperature and a temperature of an interior of the vehicle and the like.
As the atmospheric temperature decreases, a possibility of an occurrence of the cloud of the window glass increases. Thus, for example, the conventional apparatus sets the predetermined time such that the predetermined time increases as the atmospheric temperature decreases (for example, see JP 2004-210153 A).
In general, when the switch is operated while the energization control is not executed, the execution of the energization control is started and at the same time as the start of the execution of the energization control, the energization of the electric heating wire is started. The user of the vehicle operates the switch to start the energization of the electric heating wire when the user wishes to start the energization of the electric heating wire. Thus, it is natural that the energization of the electric heating wire is started at the same time as the operation of the switch. However, when the energization control is built such that the energization of the electric heating wire is started at the same time as the operation of the switch, following problems may arise.
For example, the user of the vehicle may operate the switch to start the execution of the energization control immediately after the user operates the switch to stop the execution of the energization control while the electric heating wire is energized. In this case, if the energization control is built such that the energization of the electric heating wire is started at the same time as the operation of the switch, the energization of the electric heating wire substantially continues although the energization of the electric heating wire is stopped for an extreme short time.
Further, the user of the vehicle may operate the switch to stop the execution of the energization control immediately after the energization of the electric heating wire is stopped and then, the user may operate the switch to start the execution of the energization control immediately after the user operates the switch to stop the execution of the energization control. In this case, also, the energization of the electric heating wire substantially continues with an extreme short energization stop period.
When the energization of the electric heating wire substantially continues with the extreme short energization stop period, temperatures of the electric heating wire, the window glass and the like may increase excessively and thus, a heat deterioration of the electric heating wire, the window glass and the like may occur.
In this connection, if the energization control is built so as not to start the energization of the electric heating wire when the user operates the switch to start the execution of the energization control and the temperatures of the electric heating wire, the window glass and the like detected by temperature sensors are high and then, to start the energization of the electric heating wire when the temperatures of the electric heating wire, the window glass and the like detected by the temperature sensors decrease to a certain temperature, an occurrence of the heat deterioration in the electric heating wire, the window glass and the like can be prevented. In this case, the temperature sensors increase a manufacturing cost of the conventional apparatus.
The present invention has been made for solving the aforementioned problems. An object of the present invention is to provide a window glass heating apparatus configured to start the energization of the electric heating wire when an energization permission condition for permitting the energization of the electric heating wire is satisfied and stop the energization of the electric heating wire when a predetermined time has elapsed after starting the energization of the electric heating wire or when the energization permission condition becomes unsatisfied even before the predetermined time has elapsed, thereby decreasing a possibility of an occurrence of a heat deterioration of the electric heating wire, the window glass and the like with a simple and low cost manner.